An ATP stimulated DNA-synthesizing complex of molecular weight about 390,000 has been isolated from E. coli. The complex contains DNA polymerase I and the recBC enzyme. It appears that the ATPase function and not the DNase function of the recBC enzyme is responsible for the ATP stimulated polymerase activity of the complex. The complex can be dissociated in high salt. Preliminary experiments indicate that the complex can be constructed from its component enzymes. Evidence for DNA-synthesizing complexes containing DNA polymerases II and III has also been obtained.